// 类型别名：type
type MyNumber = number
const age: MyNumber = 18


type IdType = number | string
function printID(id: IdType) {
  console.log(id)
}

type CoordinateType = {
  x: number,
  y: number,
  z?: number
}
function printCoordinate(point: CoordinateType) {
  console.log(point.x, point.y, point.z)
}